1. Field of the Invention
The present invention relates to an electron-beam projection lithography (EPL) system. More particularly, the present invention relates to an electron-beam focusing apparatus for controlling a path of an electron beam emitted from an electron-beam emitter and an EPL system using the same.
2. Description of the Related Art
During a semiconductor manufacturing process, various lithographic techniques are employed to form a desired pattern on a surface of a substrate. Conventional optical lithography using light, such as ultraviolet rays, has a limit with respect to a line width that can be implemented with such a technique. For this reason, next generation lithography (NGL) techniques have been recently proposed, by which more miniaturized and integrated semiconductor integrated circuits (ICs) having nano-scale line widths can be realized. Examples of the NGL techniques include electron-beam projection lithography (EPL), ion projection lithography (IPL), extreme ultraviolet lithography (EUVL), and proximity X-ray lithography.
Among the NGL systems, EPL systems for patterning an electron-resist coated on a substrate to be processed into a desired form using electron-beams emitted from an emitter are currently in wide use since they have a simple structure and it is easy to implement a large-area electron-beam emitter.
FIG. 1 schematically illustrates a configuration of a conventional electron-beam projection lithography system including a vacuum chamber 10 in which a wafer 30 is processed. Since an interior of the vacuum chamber 10 is maintained at a predetermined vacuum pressure by a vacuum pump 60, the vacuum chamber 10 is usually made of a steel plate having a high strength.
An electron-beam emitter 20 for emitting electron beams is disposed within the vacuum chamber 10. The wafer 30 to be processed is spaced a predetermined distance apart from the electron-beam emitter 20. A mask 22 having a predetermined pattern is located on a surface of the electron-beam emitter 20 so that the electron beam is emitted by the emitter 20 through a portion exposed by the mask 22. The electron beam thus emitted is used to pattern an electron resist 32 coated on the surface of the wafer 30 in the same pattern as the exposed surface of the emitter 20.
A heater 40 for heating the emitter 20 for emission of electron beams is placed at a rear side of the electron-beam emitter 20. In addition to heating by the heater 40, there are various alternate mechanisms for emitting electron beams from the emitter 20. Depending on the mechanism used, the structure and materials of the emitter 20 may vary.
Electrode plates 51 and 52 are disposed within the vacuum chamber 10 above and below the emitter 20 and wafer 30, respectively, for creating an electric field between the emitter 20 and wafer 30. External magnets 71 and 72 are placed above and below the vacuum chamber 10 for creating a magnetic field in the vacuum chamber 10. The electrode plates 51 and 52 and the external magnets 71 and 72 create electric and magnetic fields between the emitter 20 and the wafer 30, thereby controlling a path of an electron beam emitted from the emitter 20. More specifically, this arrangement makes it possible to focus the electron beam onto a correct position of the electron resist 32 coated on the wafer 30.
In a conventional EPL system described above, since the vacuum chamber 10 is separated from the external magnets 71 and 72, only the vacuum chamber 10 is vibrated due to vibration of the vacuum pump 60. In this case, paths of electron beams emitted from the emitter 20 are curved, thereby making it difficult to form a pattern having a nanometer-scale line width.
Another drawback of a conventional EPL system is that since the vacuum chamber 10 is manufactured from a ferromagnetic material, such as a steel plate, a magnetic flux created by the external magnets 71 and 72 is not concentrated between the emitter 20 and the wafer 30, but rather leaks through the vacuum chamber 10. Thus, it is difficult to create a uniform electric field between the emitter 20 and the wafer 30. Further, the manufacturing cost is high because the system requires the use of very large external magnets 71 and 72 to create a magnetic field of sufficient strength.